In the field of heavy construction, including the construction of steel frameworks for buildings, large assembled structures are typically hoisted into place by a crane. Referring to prior art FIG. 1, the construction site 10 of a typical building includes a building grid 12 having a number of regularly spaced positions at which steel girders are installed. Construction of the building proceeds with the installation of vertical columns 18 in these regularly spaced positions and bays 14. The bays 14 comprise a line beam 16 that extends in a horizontal orientation on top of the vertically oriented columns 18. Tie joists 20 extend generally perpendicular to the line beams to provide further support to the vertical columns 18. Each bay 14 provides the underlying support structure for a joist 24 which will support a particular floor of the building.
The joists 24 are delivered in bundles to the construction site 10 and are assembled into joist sections 28 on a joist table 26 which provides an aid to workers in spacing and assembly. A crane 22--which is disposed on or near the construction site and, usually, within the building structure itself--is used to hoist the joist sections 24 to a position on top of the line beams 16.
Referring additionally to prior art FIG. 2, each joist section 28 includes a plurality of joists 24 which are spaced apart from one another using an X-bracing 30 which is bolted thereto and/or using welded bridging rows 32 which are welded thereto. The joists 24 extend in a parallel fashion and include joist ends 44 to provide support to the joist section 28 as it rests on the line beams 16.
As shown in FIG. 2, known methods and devices for hoisting the joist section 28 comprise a rigging 34 which includes a hoist cable 36 provided with a hook and ball assembly 38 connected to a hoist beam 40. A plurality of joist cables 42 extend from the hoist beam 40 and are attached to the joist ends 44. After the joist section 28 has been assembled on the joist table 26, the rigging 34 is attached to the joist section by workers who must attach a separate joist cable 42 to each of the joist ends 44. After the device has been lifted and put in place, workers--who are positioned on top of the line beams 16--must walk along and detach each of the joist cables 42 from the joist ends 44. Typically, two workers on top of the line beams walk along the beams unhooking the attached cables and gathering them together. Usually, a manila line will be used to hold the ends of the cables in a group or bunch. As the crane lifts the cable ends to clear the structure, the manila line will be used to play out or guide the cable ends to prevent them from falling in the joist structure as the crane lifts the assembly to clear the top of the building.
The aforementioned known methods and devices for attaching the hoist-line to the joist section present a number of problems. One problem is that these known methods and devices expose workers to hazards inasmuch as detachment of the joist cables from the joist ends is required at dangerous heights from the ground. Another problem is that the prior art methods and devices for detaching the cables and attaching the cables is cumbersome and requires a great deal of effort and time to detach the cables individually and to manage the detached cables so that they do not tangle in the joists when the crane lifts the hoist-line in order to clear the building top. There is thus a need for a device which solves the aforementioned problems.